Saturn is the sixth planet from the sun in our solar system. It is the second-largest planet in our solar system (Jupiter is the largest). It has beautiful rings that are made mostly of ice chunks (and some rock) that range in size from the size of a fingernail to the size of a car. Saturn is made mostly of hydrogen and helium gas. Saturn is visible without using a telescope, but a low-power telescope is needed to see its rings.
SIZE AND SHAPE
Saturn is about 74,898 miles (120,536 km) in diameter (at the equator at the cloud tops). This is about 9.4 times the diameter of the Earth. 764 Earths could fit inside a hollowed-out Saturn. Saturn is the most oblate (flattened) planet in our Solar System. It has a equatorial diameter of 74,898 miles (120,536 km) (at the cloud tops) and a polar diameter of 67,560 miles (108,728 km). This is a difference of about 10%. Saturn's flattened shape is probably caused by its fast rotation and its gaseous composition.
RINGS
Saturn's beautiful rings are only visible from Earth using a telescope. They were first observed by Galileo in the 17th century. Saturn's bright rings are made of ice chunks (and some rocks) that range in size from the size of a fingernail to the size of a car. Although the rings are extremely wide (over 1 million km in diameter), they are very thin (about 0.6 miles = 1 km thick).
MASS, GRAVITY AND DENSITY
Saturn's mass is about 5.69 x 1026 kg. Although this is 95 times the mass of the Earth, the gravity on Saturn is only 1.08 times the gravity on Earth. This is because Saturn is such a large planet (and the gravitational force a planet exerts upon an object at the planet's surface is proportional to its mass and to the inverse of its radius squared). A 100 pound person would only weigh 108 pounds on Saturn.
Saturn is the only planet in our Solar System that is less dense than water. Saturn would float if there were a body of water large enough!
LENGTH OF A DAY AND YEAR ON SATURN
Each day on Saturn takes 10.2 Earth hours. A year on Saturn takes 29.46 Earth years; it takes 29.46 Earth years for Saturn to orbit the sun once. ORBIT AND DISTANCE FROM THE SUN
Saturn is 9.539 AU, on average, from the sun, about 9 and a half times as far from the Sun as the Earth is. At aphelion (the place in its orbit where Saturn is farthest from the Sun), Saturn is 1,503,000,000 km from the Sun. At perihelion (the place in its orbit where Saturn is closest to the Sun), Saturn is 1,348,000,000 km from the Sun.
TEMPERATURE ON SATURNThe mean temperature on Saturn (at the cloud tops) is 88 K (-185° C; -290° F).
MOONS
Saturn has dozens of moons (33 discovered as of August, 2004). It has 18 named moons. including Titan (the largest), Rhea, Iapetus, Dione, Tethys, Enceladus, Mimas, Hyperion, Phoebe, Janus, Epimetheus, Pandora, Prometheus, Helene, Telesto, Atlas, Calypso, and Pan (the smallest named moon of Saturn). At least a dozen others have been noted (but not named yet).
SPACECRAFT VISITS
Saturn has been visited by Pioneer 11 (in 1979) and by Voyager 1 and Voyager 2. Cassini, a spacecraft named for the divisions in Saturn's rings, is on the way and will arrive in 2004.
SATURN-EARTH COMPARISON
SATURN'S NAME AND SYMBOL
 This is the symbol of the planet Saturn. |
| INSIDE SATURN |  |
ATMOSPHERE AND PLANETARY COMPOSITION
Saturn is about 97% Hydrogen gas, about 3% helium gas and about 0.05% methane, plus ammonia. Near the equator, tremendous winds blow at 1,100 mph (500 meters per second) toward the east. The clouds in the atmosphere are cold, thick and uniform in shape. Saturn is a gaseous planet with a rocky core, a liquid metallic hydrogen layer above the core, and a molecular hydrogen layer above that. The hot, heavy, rocky core has a radius possibly three times the radius of the Earth.
Saturn has a strong magnetic field (less than Jupiter's, but still very strong). Saturn's magnetic field is probably generated by electrical current in conductive layers near the quickly-rotating planet's core. Because of this strong magnetic field, there are abundant auroras on Saturn and radios emissions from it.
Saturn radiates 79% more energy than it receives from the Sun, probably heat from its hot core.
| SATURN'S RINGS | |
RINGS
Saturn's beautiful rings are only visible from Earth using a telescope. They were first observed by Galileo in 1610 (using his 20-power telescope). The rings are divided into 8 major ring divisions. There are two main sections (called rings A and B) plus the smaller ring (Ring C or the Crepe ring), D and F rings; the larger gap in the rings is called the Cassini division; the smaller one is the Encke division. Starting closest to Saturn, the rings and divisions are: D, C, B, The Cassini Division, A, the Encke division, and F (subdivided into G and E, and a ring with visible clumps of matter, called knots). A huge, distant eighth ring tilted 27 degrees from the planet's main ring plane was discovered in 2009.  Saturn's moon Prometheus and Pandora, shepherding Saturn's narrow, outer F Ring. |
| Ring/Gap | Start radius (km) from the center of Saturn | End radius (km) | Width (km) |
|---|---|---|---|
| D | 67,000 km | 74,500 km | 7,500 km |
| C | 74,500 km | 92,000 km | 17,500 km |
| Maxwell Gap | 87,500 km | 87,770 km | 270 km |
| B | 92,000 km | 117,500 km | 25,500 km |
| Cassini Division | 117,500 km | 122,200 km | 4,700 km |
| A | 122,200 | 136,800 | 14,600 |
| Encke Gap | 133,570 km | 133,895 | . |
| Keeler Gap | 136,530 | 136,565 | 35 |
| F | 140,210 | 140,240-140,710 | 30-500 km |
| G | 165,800 | 173,800 | 8,000 |
| E | 180,000 | 480,000 | 300,000 |
| ? | 5.95 million | 17.85 million | 11.9 million |
| SATURN'S MOONS |
The moons of Saturn in order of distance from Saturn:
| Moon | Discovery Distance from the center of Saturn (km) Orbital period (Earth days) | Radius (km) Mass (kg) |
|---|---|---|
| Pan | Discovered: Mark R. Showalter/Voyager 2, 1990 Distance from Saturn: 133,583km Orbital period: 0.5750 day | Radius: 10 km Mass: unknown |
| Located within the Encke Gap in the rings | ||
Atlas | Discovered: R. Terrile/Voyager 1, 1980 Distance from Saturn: 137,670km Orbital period: 0.6019 day | Radius: 18.5x17.2x13.5 km Mass: unknown |
| A shepherd satellite for Saturn's A-ring. | ||
Prometheus | Discovered: S. A. Collins & D. Carlson/Voyager 1, 1980 Distance from Saturn: 139,353km Orbital period: 0.613 day | Radius: 74x50x34 km Mass: unknown |
| A shepherd satellite for the inner edge of Saturn's F Ring. | ||
Pandora | Discovered: S. A. Collins & D. Carlson/Voyager 1, 1980 Distance from Saturn: 141,700km Orbital period: 0.6285 day | Radius: 55x44x31 km Mass: unknown |
| A shepherd satellite for the outer edge of Saturn's F Ring. | ||
Epimetheus | Discovered: R. Walker/1966 and J. Fountain, S. Larson/1978 Distance from Saturn: 151,422km Orbital period: 0.694 day | Radius: 69x55x55 km Mass: 5.4 x 10 17kg |
| Covered by grooves, valleys, and craters over 30 km in diameter. Shares orbit with Janus (they are only separated by about 50 kilometers (31 miles)). Once every four years they approach each other, exchange some momentum and switch orbits. | ||
Janus | Discovered: Audouin Dollfus, 1966 Distance from Saturn: 151,472km Orbital period: 0.694 day | Radius: 97x95x77 km Mass: 1.92 x 10 18kg |
| Heavily cratered (craters over 30 km in diameter). Shares orbit with Epimetheus (they are only separated by about 50 kilometers (31 miles)). Once every four years they approach each other, exchange some momentum and switch orbits. | ||
Mimas | Discovered: William Herschel, 1789 Distance from Saturn: 185,520km Orbital period: 0.942 day |  Radius: 209x196x191.4 km Mass: 3.75 x 10 19kg |
| Icy, heavily-cratered surface. Huge crater, Herschel, is 80 miles (130 km) wide. Herschel's central mountain is 4 miles (6 km) tall, taller than Mount Everest. Very low temperatures (-200° C = -328°F). | ||
Enceladus | Discovered: William Herschel, 1789 Distance from Saturn: 238,020km Orbital period: 1.37 days | Radius: Radius: 256x247x244.6 km Mass: 7 x 10 19kg |
| Bright, smooth surface. Reflects almost all of the sunlight that hits it and is very cold ( -201° C = -330° F). 5 different types of terrain, suggesting a liquid interior: small craters, plains, fissures, corrugated terrain, and resurfaced areas. | ||
Tethys | Discovered: G.D. Cassini, 1684 Distance from Saturn: 294,660km Orbital period: 1.89 days | Radius: 535.6x528x526 km Mass: 6.27 x 10 20kg |
| Icy surface with craters, many cracks and plains. One huge ice trench, the Ithaca Chasma, is 40 miles (65 km) wide and extends over 3/4 of the way around the moon. A water-ice interior composition (density =1.21 gm/cm3). Surface temperature is -187° C = -305° F. | ||
Telesto | Discovered: B. Smith, H. Reitsema, S. Larson, J. Fountain, 1980 Distance from Saturn: 294,660km (leads Tethys) Orbital period: 1.89 days | Radius: 15x12.5x7.5 km Mass: unknown |
| Shares an orbit with Calypso; these 2 moons are also called the Tethys Trojans because they orbit Saturn in Tethys orbit, Telesto is 60° ahead of Tethys, Calypso is 60° behind Tethys. | ||
Calypso | Discovered: B. Smith, H. Reitsema, S. Larson, J. Fountain, 1980 Distance from Saturn: 294,660km (trails Tethys) Orbital period: 1.89 days | Radius: 15.0x8.0x8.0 km Mass: unknown |
| Shares an orbit with Calypso; these 2 moons are also called the Tethys Trojans because they orbit Saturn in Tethys' orbit, Telesto is 60° ahead of Tethys, Calypso is 60° behind Tethys. | ||
Dione | Discovered: G.D. Cassini, 1684 Distance from Saturn: 377,400 km Orbital period: 2.74 days | Radius: 560 km Mass: 1.10 x 10 21kg |
| Icy surface with craters, plains and streaks of bright material. Some craters over 100 km wide. Its density is 1.43 gm/cm3, the densest moon of Saturn, indicating a large rocky core. | ||
Helene | Discovered: P. Laques & J. Lecacheus, 1980 Distance from Saturn: 377,400 km (leads Dione) Orbital period: 2.74 days | Radius: 18x16x15 km Mass: unknown |
| Shares orbit with Dione, leads it by 60°. | ||
Rhea | Discovered: G.D. Cassini,1672 Distance from Saturn: 527,040 km Orbital period: 4.52 days | Radius: 764 km Mass: 2.31 x 1021kg |
| Icy surface with craters, plains and bright streaks. No atmosphere. Its density is 1.33 gm/cm3, indicating a small, rocky core covered with water-ice. | ||
Titan | Discovered: C. Huygens, 1655 Distance from Saturn: 1,221,830 km Orbital period: 15.9 days | Radius: 2,575 km Mass: 1.3455 x 10 23kg |
| Biggest moon of Saturn and second largest moon in Solar System (after Jupiter's Ganymede). It is larger than the planets Mercury and Pluto. Titan has a thick mostly nitrogen atmosphere (with some methane) and an atmospheric pressure of 1.6 bars (60 percent greater than the Earth's). This atmosphere with its heavy clouds obscures the moon's surface. It may rain liquid methane. The surface temperature is about -178°C = -289°F. | ||
Hyperion | Discovered: W. & G. Bond/W. Lassell, 1848 Distance from Saturn: 1,481,100 km Orbital period: 21.27 days | Radius: 180x140x112.5 km Mass: 2 x 10 19kg |
| Hyperion is the largest-known irregular-shaped body. It has a reddish color. Surface marred with craters. Variable rotational period. | ||
Iapetus | Discovered: G.D. Cassini,1671 Distance from Saturn: 3,561,300 km Orbital period: 79.33 days | Radius: 718 km Mass: 1.6 x 10 21kg |
| A rocky moon that is partly bright and partly reddish in color. Craters on surface. | ||
Phoebe | Discovered: W. Pickering, 1898 Distance from Saturn: 12,952,000 km Orbital period: 550.48 days (retrograde orbit) | Radius: 110 km Mass: 4 x 10 18kg |
| Almost circular shape, reddish color. Orbits in a retrograde direction (opposite in direction to other satellites' orbits). Rotates on its axis every 9 hours (this is unlike the other moons of Saturn, except Hyperion, which always show the same face to Saturn). Phoebe may be a captured asteroid. | ||
| Moon | Discovery Distance from the center of Saturn (km) Orbital period (Earth days) | Radius (km) Mass (kg) |
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